Carbodiimides and processes therefor

ABSTRACT

Processes are provided for making polycarbodiimides with high carbodiimide contents from isocyanates, and for selectively making mixed aryl-tertiary carbodiimides from isocyanates. Also provided are carbodiimides containing alpha-methylstyryl groups, and polymers made therefrom. All of these polymers and compounds are useful in coatings, and for other applications.

This invention provides selected alpha-methylstyryl substitutedcarbodiimides and polymers thereof. This invention also provides aprocess for selectively making tertiary-aryl carbodiimides, and aprocess for making polymeric carbodiimides with high carbodiimidecontents.

Carbodiimides are known in the art, and generalized processes for makingthem from isocyanates are also known. It is also known in general thatthese processes are catalyzed by certain compounds, particularlyselected phosphorous and arsenic compounds. However, these processesoften have drawbacks, such as the inability to control the productsobtained when more than one isocyanate is used, and particularly forpolymeric carbodiimides, the ability to produce polymers with highcarbodiimide contents.

U.S. Pat. No. 4,137,386 discloses the preparation of polystyrenepolymers containing dihydrocarbyl arsyl oxide radicals attached to thepolymer chain. These polymers are reported to be catalysts for theconversion of organic isocyanates to carbodiimides.

A useful review of polycarbodiimides is K. Wagner, et al., Angew. Chem.Int. Ed. Engl., vol. 20, 819-830 (1981).

SUMMARY OF THE INVENTION

This invention concerns a compound of the formula ##STR1## wherein R¹ ishydrocarbyl, and provided that the isopropenyl group is in the 3 or 4position of the benzene ring.

This invention also concerns a polymer, comprising the repeat unit##STR2## wherein R¹ is hydrocarbyl, and provided that the benzene ringis attached to the main polymer chain at the 3 or 4 position of thebenzene ring.

The invention also provides a process for the preparation oftertiary-aryl carbodiimides, comprising, contacting a tertiaryisocyanate, an aryl isocyanate, and a catalyst for the condensation ofisocyanates to carbodiimides, at a sufficiently high temperature and fora sufficient amount of time to convert the isocyanates to carbodiimide,and provided that the selectivity for the tertiary-aryl carbodiimide isgreater than it is for random reaction.

This invention also concerns a process for making polymericcarbodiimides, comprising, contacting one or more diisocyanates with atriarylarsine oxide, at a sufficiently high temperature and for asufficient amount of time to react of 90% or more of the originalisocyanate groups, and provided that the total of primary and secondaryisocyanate groups present is at least 10% of the total isocyanate groupspresent.

DETAILS OF THE INVENTION

In the compound of the formula ##STR3## R¹ is hydrocarbyl. Byhydrocarbyl herein is meant a monovalent radical containing only carbonand hydrogen. It is preferred if R¹ (in both the monomeric compound andpolymer herein) contains 1-25 carbon atoms and more preferred if R¹ isalkyl containing 1 to 6 carbon atoms, cyclohexyl, or aryl. It is mostpreferred if R¹ is phenyl, isopropyl and cyclohexyl. These monomericcarbodiimides can be made by known methods, such as the phospholeneoxide or triarylarsine oxide catalyzed condensation of the correspondingisocyanates (see Examples 1-6, herein), or dehydration of thecorresponding ureas (see for example K. Kondo, et al., Technol. Rep.Osaka Univ., vol. 25, 487-489 (1975) or H. Kamagawa et al., Bul. Chem.Soc. Japan., vol. 52, 533-535 (1979). The monomeric carbodiimidescontaining alpha-methylstyryl groups are useful as monomers for thepreparation of polymers (see below).

These alpha-methylstyryl group containing carbodiimides may bepolymerized by free radical polymerization to form polymers with therepeat unit shown above. They may be homopolymerized or copolymerized,so the term "comprising" for these polymers includes both homopolymersand copolymers. Copolymerization may be carried out with comonomers thatnormally copolymerize with alpha-methylstyrene, and these comonomers areknown in the art. Preferred comonomers are styrene, maleic anhydride,itaconic anhydride, and acrylic (including methacrylic) esters. Thepolymerizations are carried out according to known procedures.

Polymers containing units derived from the alpha-methylstyryl groupcontaining carbodiimide are reactive with compounds and groupscontaining active hydrogen atoms, such as water, hydroxyl (alcohols),carboxyl, phosphoric acid and partial esters thereof, and primary andsecondary amino. Therefore they are useful as polymeric dehydratingagents, or can be used to crosslink other polymers which contain theabove mentioned functional groups, particularly carboxyl and primary andsecondary amino. This ability to crosslink polymers containing activehydrogen makes these carbodiimide polymers useful in coatings, where itis common to form a crosslinked coating by mixing two mutually reactivepolymers which crosslink each other to form the final polymer coating.They are particularly useful in coatings for automobiles. They are alsouseful in wood finishes, and as ingredients in printing inks,photoresists, and for polymer film coatings such as photographic filmcoatings and coatings for fibers.

Also disclosed herein is a process for the production of tertiary-arylcarbodiimides from tertiary and aryl isocyanates. Throughout thisApplication, the following terms are used:

primary isocyanate or carbodiimide--An isocyanate in which the nitrogenatom is bound to a primary alkyl carbon atom (a carbon atom bound toonly one other carbon atom), or a carbodiimide in which one of thenitrogen atoms of the carbodiimide group is bound to a primary carbonatom.

secondary isocyanate or carbodiimide--An isocyanate in which thenitrogen atom is bound so a secondary (cyclo)alkyl carbon atom (a carbonatom bound to only two other carbon atoms), or a carbodiimide in whichone of the nitrogen atoms of the carbodiimide group is bound to asecondary (cyclo)carbon atom.

tertiary isocyanate or carbodiimide--An isocyanate in which the nitrogenatom is bound to a tertiary (cyclo)alkyl carbon atom (a carbon atombound to three other carbon atoms), or a carbodiimide in which one ofthe nitrogen atoms of the carbodiimide group is bound to a tertiary(cyclo)alkyl carbon atom.

aryl isocyanate or carbodiimide--An isocyanate in which the nitrogenatom is bound to a carbon atom of an aromatic ring, or a carbodiimide inwhich one of the nitrogen atoms of the carbodiimide group is bound to acarbon atom of an aromatic ring.

Since a carbodiimide group has two nitrogen atoms, the complete moleculewill require a designation of the groups on both of the nitrogen atoms,such as a tertiary-aryl carbodiimide, a ditertiary carbodiimide, etc.

Carbodiimides can be made by the condensation of isocyanate groups, andthis is usually done in the presence of a catalyst. When two differentisocyanates, R² NCO and R³ NCO, of equal reactivity are used inequimolar amounts, one expects a mixture of carbodiimides R² NCNR², R²NCNR³ and R³ NCNR³, in the molar ratio 1:2:1 respectively. If thereactivities of one of the isocyanates is greater than the other, oneexpects larger and larger amounts of R² NCNR² and R³ NCNR³, and lesseramounts of the "mixed" carbodiimide R² NCNR³. The amount of mixedcarbodiimide would be expected to decrease as the difference in therelative reactivities increases. Thus the maximum amount of mixedcarbodiimide normally expected would be about 50 mole percent. For thisreason, the art skilled have developed alternate syntheses of mixedcarbodiimides, such as using ureas as intermediates (see for example H.Kamogawa, et al., supra).

It has surprisingly been found that when an aryl isocyanate is mixedwith a tertiary isocyanate in the presence of a catalyst for thecondensation to carbodiimide, much higher than expected amounts of thearyl-tertiary carbodiimide are formed, and in some cases the product isrelatively pure aryl-tertiary carbodiimide. It has also been found thatwhen diisocyanates are used in this process that unique polymers mayresult. For example if a bis(aryl isocyanate) is reacted with abis(tertiary isocyanate), the product will be predominantly analternating carbodiimide copolymer, with the alternating units beingderived from the two isocyanates. More exactly, one obtains analternating polycarbodiimide in which one of the alternating units isdirectly connected to two adjacent carbodiimide groups through aromaticcarbon atoms, and the other alternating unit is directly connected totwo adjacent carbodiimide units through tertiary alkyl carbon atoms. Itis preferred if at least 80% of the units in the polymer arealternating. Similarly, if a diisocyanate containing one aryl isocyanateand one tertiary isocyanate is used, the resulting polymer will be onein which the monomeric units are attached to one another in apredominantly head to tail fashion.

This process is carried out in the presence of catalyst for thecondensation of isocyanates to carbodiimides, and these are known in theart (see for example K. Wagner, et al., supra). Preferred catalysts inthe process are phospholene oxides and triarylarsine oxides. The processis carried out at a sufficient temperature and for a sufficient amountof time so that the condensation to carbodiimide is accomplished. Thiswill vary according to the isocyanates and catalyst used, and can beeasily determined for any set of reactants. A convenient temperaturerange is about 0° C. to about 250° C., preferably about 120° C. to about160° C. The progress of the reaction can be monitored by a variety oftechniques, for example infrared spectroscopy. In order to avoiddecomposing either the starting materials or products the reactionshould be carried out in the absence compounds containing activehydrogen, such as water. This is conveniently done by carrying out theprocess under an inert gas such as nitrogen. Although inert solvents maybe used, it is preferred if the process is carried out without solventwhen monomeric compounds are being made.

Aryl isocyanates useful in this process include, but are not limited to,phenyl isocyanate, bis(4-isocyanatophenyl)methane, diisocyanatobenzene,and 2,4-toluenediisocyanate. 2,4-Toluenediisocyanate is a preferredaromatic isocyanate. Useful tertiary isocyanates include, but are notlimited to, t-butylisocyanate, 1,4-bis (2-isocyanato-2-propyl)benzene,2- (3-isopropenylphenyl)-2-isocyanatopropane, 2-(4-isopropenylphenyl)-2-isocyanatopropane, and 1,3-bis(2-isocyanato-2-propyl) benzene. A preferred polymer product is oneobtained from 1,3- or 1,4-bis (2-isocyanato-2-propyl)benzene and bis(4-isocyanatophenyl) methane.

The aryl-tertiary mono- and polycarbodiimides are useful as drying anddehydrating agents. In addition, reaction of these compounds with onemole of carboxylic acid per equivalent of carbodiimide leads to aN-aryl-N-acyl-N'-tertiaryalkylurea, which upon thermolysis yields anN-arylamide and a tertiary isocyanate [see Y. Iwakura, et al., Polym.Lett., vol. 6 p. 517-522 (1968)]. These aryl-tertiary carbodiimides,after reaction with carboxylic acid, give compounds which are maskedalkyl isocyanates. Alkyl isocyanates (and their reaction products) areparticularly useful in coatings, where they are very resistant to colorchange. When a polycarbodiimide is used to make theN-aryl-N-acyl-N'-tertiaryalkylurea, the product after thermolysis is abis(tertiaryisocyanate) which can be used to crosslink polymers withfunctional groups that react with isocyanates. The advantage of usingthe N-aryl-N-acyl-N'-tertiaryalkylurea instead of thebis(tertiaryisocyanate) directly is that the urea is generally much lesstoxic than the diisocyanate.

Also described herein is a process for making polycarbodiimides whichare suitable for use in coatings. Polycarbodiimides are useful incoatings because carbodiimide groups react with many functional groupssuch as carboxylic acid, alcohols and primary and secondary amines, andcan crosslink polymers which contain these functional groups.Crosslinking of such polymers is often the curing step for coatings.Carbodiimides are toxic, so it is preferable if the carbodiimides are inpolymeric form to reduce their vapor pressure (these coatings are oftenapplied as sprays).

In the instant process, a triarylarsine oxide is used as the catalyst.Useful triarylarsine oxides include, but are not limited to,triphenylarsine oxide, tri-p-tolylarsine oxide, trinaphthylarsine oxide,tris[(4-phenyl)phenyl]arsine oxide, and polymer bound arsine oxides.Triphenylarsine oxide is a preferred catalyst. Although not critical,the amount of catalyst used can range from about 0.0001% to about 3% byweight of the isocyanate compounds initially present, preferably about0.01% to about 0.5% by weight of the isocyanate compounds initiallypresent.

The isocyanates used in the process will generally be diisocyanates.Small amounts of monoisocyanates may be present to act as an endcappingagent. Endcapping agents are used to provide nonisocyanate ends to thepolycarbodiimides, see for example T. W. Campbell, et. al., J. Org.Chem., vol. 28, p. 2069-2075 (1963), for a discussion of endcapping ofpolycarbodiimides. Any diisocyanates may be used in the process. Usefuldiisocyanates include, but are not limited to,bis(4-isocyanatophenyl)methane, 2,4-toluenediisocyanate1,4-bis(2-isocyanato-2-propyl)benzene,1,3-bis(2-isocyanato-2-propyl)benzene, 1,2-, 1,3- and1,4-diisocyanatocyclohexane, 1,6-hexanediioscyanante, isophoronediisocyanate, trimethyl-1,6-hexanediisocyanate, andbis(4-isocyanatocyclohexyl)methane.

The process is carried out at a temperature of 0° C. to 300° C.,preferably about 20° C. to about 200° C., and more preferably about 100°C. to about 160° C. Although not necessary, the process may be carriedout in the presence of an inert solvent. Examples of suitable solventsare propylene glycol methyl ether acetate, xylene, toluene, propylacetate, butyl ether, chlorobenzene, o-dichlorobenzene, anddichloroethylene. It is preferred if a solvent is present. Solventscontaining active hydrogen atoms (e.g., alcohols) should not be used. Itis preferred that the final product is soluble in solvents, i.e., hasnot gelled, since soluble polycarbodiimides are preferred for use incoatings. Process times will vary according to the isocyanates used, theproduct desired, the type and amount of catalyst used, the temperature,etc. Generally process times will range from 0.1 to 24 hr., typically 1to 10 hr. The reaction may be followed by a variety of techniques, forexample infrared spectroscopy.

Compounds containing active hydrogen, such as water vapor, aredeleterious, so it is convenient to carry out the process under an inertgas such as nitrogen or dry air.

In the instant process at least 10% of the total initial isocyanategroups are primary and/or secondary isocyanates, that is the total ofthe primary and secondary isocyanates are at least about 10% of theinitial isocyanate groups. It is preferred if 25% of the initialisocyanates groups are primary and/or secondary isocyanates, and morepreferred if at least about 50% of the initial isocyanates groups areprimary and/or secondary isocyanate groups.

In the instant process it has been found that the resultingpolycarbodiimide has a relatively high carbodiimide content. It ispreferred if 90% or more of the original isocyanate groups are reacted,more preferably 95% or more. By original isocyanate groups are meant allof the isocyanate groups initially present minus those groups that arereacted with alcohols, etc. to endcap the polymers. Assuming completeconversion of the original isocyanate groups to carbodiimide groups, forevery two starting isocyanate groups, one should obtain one carbodiimidegroup. The reacted isocyanate groups include all isocyanate groups thatcould have formed carbodiimides, but does not include for example,isocyanate groups that are used to endcap the polymer where theendcapping reaction does not form a carbodiimide, such as reaction withan alcohol. It is known in these types of polymerizations that sidereactions reduce the actual number of carbodiimide groups in thepolycarbodiimide below that theoretically attainable. In the instantprocess it is preferred if 70% or more of the theoretical number ofcarbodiimide groups are obtained, and more preferably 90% or more. Ingeneral, it is preferred to obtain a polycarbodiimide with as high(compared to the theoretical amount) a carbodiimide content as possible.

One of the important parameters herein is the carbodiimide content of apolycarbodiimide. This is measured by the procedure described by W. Adamand F. Yany, Analytical Chemistry, vol. 49 p. 676 (1977) which isslightly modified. Usually tetrahydrofuran solutions of the reactantsare used, and the times of reaction are varied from 1 to 48 hr., thelonger times being used for hindered, somewhat insoluble, or aromaticcarbodiimides.

Reactions were typically carried out in 500 mL 3-necked round bottomflasks equipped with nitrogen inlet, bubbler outlet (equipped with anapparatus to measure gas evolved), water-cooled reflux condenser,mechanical or magnetic stirrer, thermocouples for temperaturemeasurement, septum capped inlet for addition of materials, and heatedby a heating mantle (sometimes controlled with a temperature controller)or similar apparatus.

EXAMPLE 1 1-Phenyl-3-[2-(3-isopropenylphenyl)-2-propyl]carbodiimide

We combined 0.3182 g 3-methyl-l-phenyl-2-phospholene-1-oxide (MPPO),m-TMI [2-(3-isopropenylphenyl)-2-propylisocyanate], and 19.31 g phenylisocyanate. After heating at 140°-150° C. for 14 hours, IR showed nearlycomplete conversion of isocyanates to carbodiimides. GC-MS integratedionization current shows a response of 265944 units for the title mixedproduct, 3558 units for the diphenyl carbodiimide, and 3602 units forthe ditertiarycarbodiimide. Assuming that the detector sensitivity forthe mixed product is the same, the selectivity for the mixed product isthe average of the two other products, the reaction selectivity for themixed product is 265944/(265944+3602+3558) or 97%, so the maximum yieldof either mixed product is 3%.

EXAMPLE 2 1-Phenyl-3-[2-(3-isopropenylphenyl) -2-propyl]carbodiimide

We combined 0.0982 g TPAO, 19.30 g benzyl acetate (internal standard),60.40 g of m-TMI, and 35.77 g phenyl isocyanate. Heating at 150° C. wascarried out for 6 hours; at 2 hours IR showed nearly complete conversionof isocyanates to carbodiimides. GC-FID showed that product waspredominantly the title carbodiimide (89.3%), unreacted TMI (4.2%),1,3-bis[2-(3-isopropenylphenyl-2-propyl]carbodiimide (4.2%) and1,3-diphenylcarbodiimide (2.9%) versus internal standard. Material fromthis Example was distilled to obtain in 71% recovery on products of apurified sample (92% pure) of the title product and in 6% recovery onproducts of a crude (66% purity) sample of the same product.

EXAMPLE 3 1-Isopropyl-3-[2-(3-isopropenylphenyl)-2-propyl]carbodiimide

We combined 0.0820 g TPAO, 60.46 g of m-TMI, and 12.63 g1,3-diisopropylcarbodiimide. After heating at 150° C. for 5 hours, afurther 0.0857 g TPAO was added. Heating was continued 4 further hours.IR showed complete conversion of isocyanates to carbodiimides. The mixedcarbodiimide forms about 51% molar of the product, as determined by ¹H--NMR.

EXAMPLE 4 1-Isopropyl-3-[2-(3-isopropenylphenyl)-2-propyl]carbodiimide

We combined 0.1145 g TPAO, 60.45 g of m-TMI, and 28.42 g1,3-diisopropylcarbodiimide. After heating at 150° C. for 2 hours, afurther 0.1047 g triphenylarsine oxide (TPAO) was added. Heating wascontinued 3 further hours. A further 0.1084 g triphenylarsine oxide(TPAO) was added. Heating was continued 6 further hours. IR showednearly complete conversion of isocyanates to carbodiimides. Material wasdistilled to obtain in 50% recovery a purified sample of the titleproduct, as verified by ¹ H--NMR.

EXAMPLE 5 1-Cyclohexyl-3-[2-(3-isopropenylphenyl) -2-propyl]carbodiimide

We combined 0.0804 g TPAO, 60.43 g of m-TMI, and 20.61 g1,3-dicyclohexylcarbodiimide. After heating at 150° C. for 6 hours, IRshowed nearly complete conversion of isocyanates to carbodiimides. ¹H-NMR indicated the desired product contaminated with1,3-dicyclohexylcarbodiimide, and 1,3-bis [2- (3-isopropenylphenyl)-2-propyl]carbodiimide.

Distillation provided a fraction (11% by weight) of mostlydicyclohexylcarbodiimide, and another fraction (37% by weight) of mostlythe other homocarbodiimide, and other fractions which contained allthree products. The title product constitutes less than 52% by weight ofthe product mixture.

EXAMPLE 6 1-Cyclohexyl-3-[2-(3-isopropenylphenyl)-2-propyl]carbodiimide

We combined 0.0830 g TPAO, 60.41 g of m-TMI, and 25.04 gcyclohexylisocyanate. After heating at 150° C. for 7 hours, IR showednearly complete conversion of isocyanates to carbodiimides. ¹ H--NMRindicated the desired product contaminated with1,3-dicyclohexylcarbodiimide, and1,3-bis[2-(3-isopropenylphenyl)-2propyl]carbodiimide.

EXAMPLE 7

Under nitrogen were combined 109.67 g methyl ether polyethylene oxide(average molecular weight 750 g/mole), 357.43 g isophorone diisocyanate,400.42 g propylene glycol methyl ether acetate, and 0.8246 g2-ethylhexylglycidyl ether. The mixture was refluxed for 2 hours,cooled, and 0.7159 g triphenylarsine oxide hydrate was added. Themixture was refluxed 2 hours, at which time IR demonstrated no peakaround 2200 cm⁻¹, and a strong peak around 2100 cm⁻¹. A solidsdetermination showed 50.7% solids; a carbodiimide titration showed 1.75mM/g solution. (Theory, 50%, 1.92 mM/g-solution.)

EXAMPLE 8

Under nitrogen were combined 26.5329 g isophorone diisocyanate, 1.5260 gcyclohexyl isocyanate, 22.5389 g xylenes, and 0.0077 g triphenylarsineoxide hydrate. The mixture was refluxed 3 hours, at which time IRdemonstrated no peak around 2100 cm⁻¹, and a strong peak around 2200cm⁻¹. A further 0.0327 g triphenylarsine oxide hydrate was added. Refluxwas continued another hour, then the reaction mixture was held at roomtemperature overnight. Reflux was continued 2 further hours, at whichtime IR demonstrated no peak around 2200 cm⁻¹, and a strong peak around2100 cm⁻¹.

A solids determination showed 69.9% solids (loss during reflux?); acarbodiimide titration showed 3.45 mM/g solution. (Theory, 50%, 2.78mM/g-solution; expect 3.89 at 69.9% solids.)

EXAMPLE 9

Under nitrogen were combined 35.21 g methyl ether polyethylene oxide(average molecular weight 750 g/mole), 135.76 gbis(4-isocyanatocyclohexyl)-methane, 150.12 g propylene glycol methylether acetate. The mixture was refluxed for 1 hour, cooled, and 0.1533 gtriphenylarsine oxide hydrate was added. The mixture was refluxed 3hours, at which time IR demonstrated a very small peak around 2200 cm⁻¹,and a strong peak around 2100 cm⁻¹. A solids determination showed 50.5%solids; a carbodiimide titration showed 1.65 mM/g solution. (Theory,50%, 1.72 mM/g-solution.)

EXAMPLE 10

A 500 mL 3-neck round bottom flask with nitrogen flush, mechanicalstirrer, reflux condenser, was charged with 0.2168 g triphenylarsineoxide, 71.23 g methylene bis(4-isocyanatocyclohexane), 0.87 gcyclohexylisocyanate, (expected degree of polymerization=78) and 240.07g xylene. The mixture was heated at reflux for 3 hours, at which time IRshowed no peak around 2200 cm⁻¹ for NCO, and a large peak around 2100cm⁻¹ for NCN. The product was soluble in THF, but phase-separated frompropylene glycol methyl ether acetate. The product was 20.9% solids, andhad a carbodiimide content of 0.89 mM/g. (Theory, 0.95 mM/g.)

EXAMPLE 11

Under nitrogen were combined 57.45 g methyl ether polyethylene oxide(average molecular weight 750 g/mole), 60.29 gbis(4-isocyanatocyclohexyl)methane, 50.93 g isophorone diisocyanate,57.45 g propylene glycol methyl ether acetate. The mixture was refluxedfor 2 hours, cooled, and 0.2485 g triphenylarsine oxide hydrate wasadded. The mixture was refluxed 3 hours, at which time IR demonstratedno peak around 2200 cm⁻¹, and a strong peak around 2100 cm⁻¹. A solidsdetermination showed 50.5% solids; a carbodiimide titration showed 1.34mM/g solution. (Theory, 50%, 1.40 mM/g-solution.)

EXAMPLE 12

Under nitrogen were combined 46.35 g methyl ether polyethylene oxide(average molecular weight 750 g/mole), 41.48 g tetramethyl-meta-xylylenediisocyanate, 37.82 g isophorone diisocyanate, 125.52 g propylene glycolmethyl ether acetate. The mixture was heated to 100° C. for 1.5 hours,cooled, and 0.1789 g triphenylarsine oxide hydrate and 15.50 gcyclohexyl isocyanate were added. The mixture was refluxed 4 hours, atwhich time IR demonstrated a very small peak around 2200 cm⁻¹, and astrong peak around 2100 cm⁻¹. A solids determination showed 50.0%solids; a carbodiimide titration showed 1.41 mM/g solution. (Theory,49.8%, 1.48 mM/g-solution.)

EXAMPLE 13

Under nitrogen were combined 17.24 g tetramethyl-meta-xylylenediisocyanate, 7.92 g 1,6-diisocyanatohexane, 2.98 g cyclohexylisocyanate, 25.02 g xylenes, and 0.0194 g triphenylarsine oxide hydrate.The mixture was refluxed 5 hours, and a further 0.0307 g triphenylarsineoxide hydrate was added. Reflux was continued a further 3 hours, held atroom temperature over a weekend, and continued a further 5 hours, atwhich time IR demonstrated no peak around 2200 cm⁻¹, and a strong peakaround 2100 cm⁻¹. A solids determination showed 54.5% solids; acarbodiimide titration showed 2.64 mM/g solution. (Theory, 47.3%, 3.14mM/g-solution at 54.5% solids due to solvent loss.)

EXAMPLE 14

Under nitrogen were combined 115.12 gbis(4-isocyanatocyclohexyl)methane, 24.59 g 1,6-diisocyanatohexane,0.9232 g 2-ethylhexylglycidyl ether, and 125.28 g propylene glycolmethyl ether acetate. The mixture was refluxed for 2 hours, cooled, andthere was added 12.17 g cyclohexyl isocyanate, and 0.1581 gtriphenylarsine oxide hydrate. The mixture was refluxed 4 hours, and afurther 0.0346 g triphenylarsine oxide hydrate was added. Reflux wascontinued a further 2 hours, at which time IR demonstrated no peakaround 2200 cm⁻¹, and a strong peak around 2100 cm⁻¹. A solidsdetermination showed 49.3% solids; a carbodiimide titration showed 2.29mM/g solution. (Theory, 49.9%, 2.52 mM/g-solution.)

EXAMPLE 15

In a 500 mL flask with nitrogen flushing, were placed 0.0883 gtriphenylarsine oxide, 58.98 g isophorone diisocyanate, 31.51 g phenylisocyanate, 23.03 g toluene diisocyanate, and 110.02 g xylenes. After 2hours reflux, no IR absorbance could be detected around 2200 cm⁻¹ forisocyanate. Solids was 45.6%. The back titration with oxalic acid, after24 hours reaction, showed a carbodiimide content of 2.13 mM/g, 80% oftheory.

COMPARATIVE EXPERIMENT 1

In a 500 mL flask with nitrogen flushing, were placed 0.5294 g3-methyl-l-phenyl-phospholene-l-oxide, 59.18 g isophorone diisocyanate,31.38 g phenyl isocyanate, 22.94 g toluene diisocyanate, and 110.07 gxylenes. After 2 hours reflux, some IR absorbance could be detectedaround 2200 cm⁻¹ for isocyanate. After 6 hours reflux, no peak could bedetected. Solids was 47.6%. The back titration with oxalic acid, after24 hours reaction, showed a carbodiimide content of 1.62 mM/g, 61% oftheory.

EXAMPLE 16

A mixture of bis (4,4'-diisocyanatophenyl)methane (80.47 g) ,alpha,alpha,alpha',alpha'-tetramethyl-1,3-xylylene diisocyanate (94.34g), phenyl isocyanate (7.66 g), xylene (150 g) and triphenylarsine oxide(0.2153 g) were combined under nitrogen flushing and refluxed for 5hours. Titration demonstrated a carbodiimide content of 2.46 mM/g, andsolids were 52.1 wt. %. ¹ NMR analysis demonstrated that 85-95% of themaximum amount of mixed unsymmetrical carbodiimide (alternatingcopolymer) had been formed.

¹ H-NMR resonance positions were established through comparison ofspectra of a (1) polymer of alpha,alpha,alpha',alpha'-tetramethyl-1,3-xylylene-carbodiimide, (2) biscarbodiimideof alpha, alpha,alpha',alpha'-tetramethyl-1,3-xylylenediisocyanate and 2moles of phenyl isocyanate, and the (3) monomer1-phenyl[2-(3-isopropenylphenyl)-2-propyl]carbodiimide with the product.For (1), H(2) (the hydrogen on aromatic carbon 2 of the xylylenenucleus) was at delta=7.735 PPM, while the methyl group was at 1.766.For (2), H(2) was at 7.651, and the methyl at 1.723; for (3), the H(2)was at 7.623, and the methyl was at 1. 607. From this, we conclude thatthe copolymer where two alpha,alpha,alpha',alpha'-tetramethyl-1,3-xylylgroups are joined as a carbodiimide should have 4 methyl groupsresonating around 1.601 PPM; whereas a mixed carbodiimide would showmethyl groups at around 1.7+; similarly, the H(2) should appear around7.623 (aliphatic) and 7.70±0.05 (mixed) respectively. The product showedresonances at 1.601 (relative area 2.1) and a complex pattern of 1greatly predominant peak at 1.715 (relative area 18). Similar resultswere seen in the aromatic region for H(2); a major complex at around7.725 (area 1.4), and a minor complex at around 7.667 (area 0.3);however, experimental error was much higher.

EXAMPLE 17

In a 250 mL 3-neck flask with nitrogen flushing, magnetic stirring,reflux condenser, were combined 42.35 g propylene glycol methyl etheracetate, 45.01 g isophorone diisocyanate, 4.52 g of polyethylene oxidemethyl ether (MW=750), 1.50 g n-butyl isocyanate, and 0.0826 gtriphenylarsine oxide. After 2 hours reflux at about 152° C., IR showedno isocyanate absorbance, and a very strong absorbance due tocarbodiimide. After storage for about 300 days, Gardner-Holt Viscositywas R, and carbodiimide content was 2.2 mM/(gram solution), versus atheoretical yield of 2.4 mM/(gram solution), without correction for anyloss of volatiles.

COMPARATIVE EXAMPLE 2

In a 250 mL 3-neck flask with nitrogen flushing, magnetic stirring,reflux condenser, were combined 38.28 g propylene glycol methyl etheracetate, 45.44 g isophorone diisocyanate, 4.56 g of polyethylene oxidemethyl ether (MW=750), 1.51 g n-butyl isocyanate, and 4.70 g of 10%3-methyl-l-phenyl-2-phospholene-l-oxide in xylene. After 4 hours refluxat about 152° C., IR showed a substantial isocyanate absorbance, about25% of the size of the strong absorbance due to carbodiimide. At 7 hoursreflux, this peak was still easily recognized, as about 4% of the strongcarbodiimide peak. After 11 hours of reflux, the reaction mixturegelled.

EXAMPLE 18

In a 100 mL flask with nitrogen flush, mechanical stirrer, refluxcondenser, were placed 0.0859 g triphenylarsine oxide, 33.4560 gisophorone diisocyanate, 1.4919 g n-butyl isocyanate, and 25.0234 gpropylene glycol methyl ether acetate. The mixture was refluxed at about145° C. for 1 hour, when IR showed the isocyanate peak to be about 4% ofthe carbodiimide peak. Soon after, the solution was cooled, and 8 dayslater was noted to be an easily-flowing liquid.

COMPARATIVE EXAMPLE 3

In a 100 mL flask with nitrogen flush, mechanical stirrer, refluxcondenser, were placed 33.5565 g isophorone diisocyanate, 1.4616 gn-butyl isocyanate, 25.5440 g propylene glycol methyl ether acetate, and8.0 g of 10% 3-methyl-l-phenyl-2-phospholene-l-oxide in xylene. Themixture was refluxed at about 145° C. for 8 hours, at which time asignificant concentration of isocyanate could be detected by IR. Whenthe viscous liquid was allowed to cool, it gelled.

EXAMPLE 19

A 1 liter flask was sparged with nitrogen at 40 mL/min. Isophoronediisocyanate (181.51 g), xylenes (14.34 g) and triphenylarsine oxide (0.1442 g) were charged. The contents were heated to ca. 145° C., at whichtime gas evolution of up to 760 mL/min was noted, as measured by aSierra Instruments Top-Trak mass flowmeter calibrated to air. After lessthan 50 minutes, the flask contents were cooled to less than 60° C.,effectively stopping gas generation after evolution of ca. 12 liters ofgas. n-Butanol (15.71 g), methyl ether of polyethylene oxide (MW=750nominal) (116.54 g), and propylene glycol methyl ether acetate (234.75g) were added; separately toluene diisocyanate (56.96 g) and furtherpropylene glycol methyl ehter acetate (130.0 g) were also added. Thecontents were heated to ca. 110° C. for 1 hour, then raised to ca.146°-150° C. for 3.5 hours. IR showed complete conversion of isocyanategroups. Gardner-Holt bubble tube viscosity was A to A-1, solids was47.1%, and carbodiimide content by oxalic acid back titration was0.82±0.02 mM/g. Theoretical yield is 1.356 mM/g.

COMPARATIVE EXAMPLE 4

A 1 liter flask was sparged with nitrogen at 40 mL/min. Isophoronediisocyanate (181.55 g), and a solution of 10 wt. % MPPO in xylenes(14.31 g) were charged. The contents were heated to ca. 145° C., atwhich time gas evolution of up to 180 mL/min was noted, as measured by aSierra Instruments Top-Trak mass flowmeter calibrated to air. Afterabout 2 hours, the flask contents were cooled, effectively stopping gasgeneration after evolution of ca. 12.4 liters of gas. n-Butanol (15.71g), methyl ether of polyethylene oxide (MW=750 nominal) (116.53 g), andpropylene glycol methyl ether acetate (234.02 g) were added; separatelytoluene diisocyanate (56.91 g) and further propylene glycol methyl etheracetate (130.0 g) were also added. The contents were heated to ca. 110°C. for 1 hour, then raised to ca. 146°-150° C. for 11 hours. IR showedalmost complete conversion of isocyanate groups. Gardner-Holt bubbletube viscosity was A-1, solids was 47.2%, and carbodiimide content byoxalic acid back titration was 0.63 mM/g. Theoretical yield is 1.358mM/g.

What is claimed is:
 1. A process for the preparation of tertiary-arylcarbodiimide, comprising, contacting a tertiary isocyanate, an arylisocyanate, and a catalyst for the condensation of isocyanate tocarbodiimide, at a sufficiently high temperature and for a sufficientamount of time to effect conversion of the isocyanates to carbodiimide,and provided that the selectivity for the tertiary-aryl carbodiimide isgreater than it is for random reaction.
 2. The process as recited inclaim 1 wherein said catalyst is a phospholene oxide or a triarylarsineoxide.
 3. The process of claim 1 conducted at a temperature of about 0°C. to about 250° C.
 4. The process as recited in claim 1 wherein saidaryl isocyanate is phenyl isocyanate, bis(4-isocyanatophenyl)methane,diisocyanatobenzene, or 2,4-toluenediisocyanate.
 5. The process asrecited in claim 1 wherein said tertiary isocyanate ist-butylisocyanate, 1,4-bis(2-isocyanato-2-propyl)benzene,2-(3-isopropenylphenyl)-2-isocyanatopropane,2-(4-isopropenylphenyl)-2-isocyanatopropane, or1,3-bis(2-isocyanato-2-propyl)benzene.
 6. A process for making polymericcarbodiimides, comprising, contacting one or more diisocyanates with atriarylarsine oxide, at a sufficiently high temperature and for asufficient amount of time to effect reaction of 90% or more of theoriginal isocyanate groups, and provided that the total primary andsecondary isocyanate groups present is at least 10% of the totalisocyanate groups present.
 7. The process as recited in claim 6 whereinabout 0.0001% to about 3% by weight of the isocyanate compoundsinitially present of said triarylarsine oxide is present.
 8. The processas recited in claim 7 wherein about 0.01% to about 0.5% by weight of theisocyanate compounds initially present of said triarylarsine oxide ispresent.
 9. The process as recited in claim 6 wherein said polymericcarbodiimide wherein about 95% or more of the original isocyanate groupsare reacted.
 10. The process as recited in claim 6 wherein saidtemperature is 0° C. to 300° C.
 11. The process as recited in claim 10wherein said temperature is about 20° C. to about 200° C.
 12. Theprocess as recited in claim 11 wherein said temperature is about 110° C.to about 170° C.
 13. The process as recited in claim 6 wherein saidtriarylarsine oxide is triphenylarsine oxide.
 14. The process as recitedin claim 6 wherein a solvent is present.